Agent Activity feed: sidebar timeline for autonomous actions

[kovtcharov]

Summary

Add a dedicated Agent Activity section to the sidebar that shows a timeline of autonomous agent actions, separate from user-created chat sessions.

Parent issue: #555 (Autonomous mode)

Sidebar Layout

Sidebar
+----------------------------------+
| [+ New Chat]                     |
|                                  |
| AGENT ACTIVITY          3 new   |
| |- Checked deployment    2m ago  |
| |- Found new release     1h ago  |
| |- Indexed project       3h ago  |
|                                  |
| SESSIONS                         |
| |- My project chat       today   |
| |- Research notes         2d     |
| |- Budget analysis        5d     |
+----------------------------------+

Design

• Pinned, collapsible section above the session list
• Each entry: action summary + relative timestamp
• Click to expand full result details
• Badge shows count of unseen updates
• "AUTO" badge on actions in the agent activity panel
• On app open: "3 new updates from GAIA" summary

Notification Toast

When agent acts autonomously, show a subtle toast notification:
"GAIA acted on your behalf: checked deployment status - all green"

Configurable via "Activity notifications" setting (on by default).

Backend

• New table or column in chat database to store autonomous action results
• API endpoint: GET /api/agent-activity (list recent autonomous actions)
• API endpoint: PUT /api/agent-activity/{id}/seen (mark as seen)

Acceptance Criteria

• Agent Activity section in sidebar above sessions
• Collapsible with unseen badge count
• Click to expand full result
• Toast notifications for autonomous actions
• Actions stored and retrievable via API
• Seen/unseen tracking